This invention relates to the field of variable resistance devices, and more particularly to a clutch means for worm gear actuated multiple turn resistors.
In some of the prior art device (U.S. Pat. No. 3,242,452, patented March, 1966, issued to A. A. Grunwald et al), a contact supporting member is rotatably mounted in a housing and is provided with teeth and a toothless section on its periphery. There is also a U-shaped slot provided in one side of the toothless section, the teeth being arranged to engage the screwthread on a lead screw so that the rotation of the lead screw will rotate the contact supporting member. A resilient means disposed in the U-shaped slot of the toothless section comprises a U-shaped spring having two legs and a bight section with the legs extending outwardly from the member and in position to engage the thread on the lead screw as the member is rotated.
A stop means is also arranged to limit the rotation of the member in either direction when one of the legs of the U-shaped spring engages the thread of the lead screw, the portion intermediate the legs of the U-shaped slot forming a stop member for limiting flexure of the legs of the spring toward each other from an unflexed position.
Another prior art device is describe in U.S. Pat. No. 3,768,325 dated Oct. 30, 1973 in which a ratcheting mechanism for use in a worm gear actuated potentiometer, utilizes a worm gear having a circumferential portion of the teeth thereof removed, i.e. a blank area, a worm screw having threads for engaging the teeth of the worm gear, and a ratcheting structure including a stop member and a resilient member. One of the two ratcheting structure members is attached to a housing or other unmovable structure and the other is attached to the worm gear at locations such that the resilient member will engage the stop member whenever the threads of the worm screw engage a tooth of the worm gear adjacent the blank area so as to provide ratcheting.
While such prior art structures have their own merit to overcome the disadvantages of typical clutch mechanism they have also a disadvantage in that they require a separate stop mechanism in addition to a ratcheting mechanism or clutch means, which brings forth complexities in the structure thereof; the ratcheting mechanism or clutch means is somewhat unreliable and unpredictable practically after repeated usage, due to the use of strip shaped resilient member; and the device may be difficult and expensive to manufacture.